Authentication bypass is a security flaw that allows unauthorized users to gain access to a system or application without proper credentials. This can occur due to weaknesses in the authentication process, such as poorly implemented login mechanisms or predictable URLs. Attackers exploit these vulnerabilities to bypass security measures and access sensitive information. Common methods of authentication bypass include manipulating input fields, exploiting session management flaws, or using default credentials. Organizations must regularly test their systems for these vulnerabilities and implement strong security practices to protect against unauthorized access and potential data breaches.